In many circumstances, it may be desirable to set the current being fed to a component to some specific value. For instance, in the case of light emitting diodes (LEDs) an LED driving circuit is generally constructed to deliver a predetermined current to the LED.
For components that may have a certain functionality that is dependent on current, it may also be desirable to change the current being fed to the component. It may be advantageous to be able to continuously alter the current being supplied to the component. In the aforementioned case of LEDs, for example a change in the brightness or intensity of the light emitted by the LED may be called for, in which case the current should be altered.
Typical circuits for driving LEDs, also those for which LED current should be adjustable, operate with fixed voltages. This voltage is selected to be high enough to be able to drive LEDs with a current that will lead to maximum intensity of the radiation emitted by the LED. Solutions with these high voltages are problematic because extra voltage will be converted to heat somewhere in the circuit, which is unpreferable. It has also been noticed in relation to LED matrices that excess voltage may cause challenges for software that is controlling the LEDs.
Printed electronics is also becoming more widespread and may replace the use of traditional printed circuit boards (PCBs) in many cases. With the inks in printed electronics that are used for printing conductive traces, the ink has a resistivity that will lead to voltage losses in the circuit, making driving LEDs in printed electronics more challenging than in the case of traditional PCBs. This voltage loss will vary with current and is difficult to take into account for instance due to inaccuracy in the printers, traces thus not possibly even being uniform. In addition to circumstances where a circuit should be designed to deliver an adjustable current to an LED, a circuit designer should be able to calculate or estimate the aforementioned voltage losses also for circuits with non-adjustable currents, as the power consumption of the LED may vary with time. It may be difficult or in practice impossible to estimate the effect of printed ink resistance and to design a circuit that will actually deliver a desired current to the LED.
In some cases circuits may be subject to conditions that lead to continuous adjustments of currents and/or voltages, as resistances in the circuit may vary with time. For example, stretching or straining of materials may occur during manufacture or during use of a product comprising a circuit that lead to varying resistances and voltage losses that may lead to unexpected or undesired behavior of the product either with time while in use or even directly after manufacturing, due to varying or unpredictable currents through target components.